The present invention relates to a method for the preparation of a specific triazole compound. More particularly, the invention relates to a novel and efficient industrial method for the preparation of a triazole compound or, in particular, a 3-(2,4,6-trialkylphenylthio)-1H-1,2,4-triazole compound, which is useful as an intermediate in the synthetic preparation of various kinds of carbamoyl triazole-based herbicides.
As is well known, some of carbamoyl triazole derivatives have excellent herbicidal activity so that active investigations are now under way for the development of herbicides containing such a compound as the effective ingredient.
While the above mentioned carbamoyl triazole derivatives can be synthesized from a triazole derivative having an alkyl-substituted phenyl sulfide group as an intermediate, various methods have been proposed heretofore for the synthetic preparation of these intermediate compounds. For example, Japanese Patent Publication 5-73745 discloses a synthetic route via a diazonium salt starting from amino mesitylene. This method, however, is far from satisfactory as an industrial method because the yield of the product compound can rarely exceed 50% and the reaction for the preparation of the diazonium compound involves troublesome procedures if not to mention the risk of explosion in the reaction as is taught in guide books for organic syntheses that the reaction of an aromatic diazonium salt and a thiol compound involves an explosive decomposition of the diazo sulfide.
On the other hand, Japanese Patent Kokai 1-121279 proposes a method in which a triazole compound is obtained by the reaction of 3-mercapto-1H-1,2,4-triazole and a halogenobenzene unsubstituted or substituted by one or two of substituent groups selected from nitro group and trifluoromethyl group in the presence of a base. An experiment is disclosed therein according to which a reaction was performed by using 3,5-bis(trifluoromethyl) bromobenzene in the presence of a catalytic amount of copper (I) chloride in N,N-dimethylformamide as the solvent. As being motivated by this disclosure, the inventors conducted an experiment on an assumption that the reaction with a 1,3,5-trialkyl-2-halogenobenzene could hopefully proceed under similar conditions to obtain a result that the desired triazole compound could hardly be obtained in contrast to the above mentioned assumption.
The reason therefor is presumably that, when an electron-attractive group such as trifluoromethyl group or nitro group is introduced into the benzene nucleus, elimination of the halogen atom from the benzene nucleus readily proceeds to promote proceeding of the reaction so that the desired triazole compound can be obtained even by the use of N,N-dimethylformamide as the solvent while, when three lower alkyl groups as electron-donating groups are introduced into the benzene nucleus as in a 1,3,5-trialkyl-2-halogenobenzene, elimination of the halogen atom from the benzene nucleus is prevented to cause retardation of the reaction so that the desired triazole compound cannot be obtained by using N,N-dimethylformamide as the solvent.